Police suspect that the couple's son Devanand might have made them drink acid that is used for cleaning the bathroom, following an argument with them.
A case of abetment of suicide has been registered against Devanand and his wife under section 306 of the IPC as he allegedly threatened his parents Lakshmibai (55) and Ramamurthy over some family matter, including some financial issues, Alwal Police Station Inspector S V Hari Krishna said.
"After consuming the acid, Lakshmibai died last night, while Ramamurthy is in a critical condition and undergoing treatment at a government hospital, the police officer said based on a preliminary investigation.
No arrests have been made and the probe is on.